Inhomogeneous wave reflection from the surface of a partially saturated thermoelastic porous media

Purpose The purpose of this paper is to study the propagation of inhomogeneous waves in a partially saturated poro-thermoelastic media through the examples of the free surface of such media.. Design/methodology/approach The mathematical model evolved by Zhou et al. (2019) is solved through the Helmholtz decomposition theorem. The propagation velocities of bulk waves in partially saturated poro-thermoelastic media are derived by using the potential functions. The phase velocities and attenuation coefficients are expressed in terms of inhomogeneity angle. Reflection characteristics (phase shift, loci of vertical slowness, amplitude, energy) of elastic waves are investigated at the stress-free thermally insulated boundary of a considered medium. The boundary can be permeable or impermeable. The incident wave is portrayed with both attenuation and propagation directions (i.e. inhomogeneous wave). Numerical computations are executed by using MATLAB. Findings In this medium, the permanence of five inhomogeneous waves is found. Incidence of the inhomogeneous wave at the thermally insulated stress-free surface results in five reflected inhomogeneous waves in a partially saturated poro-thermoelastic media. The reflection coefficients and splitting of incident energy are obtained as a function of propagation direction, inhomogeneity angle, wave frequency and numerous thermophysical features of the partially saturated poro-thermoelastic media. The energy of distinct waves (incident wave, reflected waves) accompanying interference energies between distinct pairs of waves have been exhibited in the form of an energy matrix. Originality/value The sensitivity of propagation characteristics (velocity, attenuation, phase shift, loci of vertical slowness, energy) to numerous aspects of the physical model is analyzed graphically through a particular numerical example. The balance of energy is substantiated by virtue of the interaction energies at the thermally insulated stress-free surface (opened/sealed pores) of unsaturated poro-thermoelastic media through the bulk waves energy shares and interaction energy.

Verification of the electromagnetic deep-penetration effect in the real world

The deep penetration of electromagnetic waves into lossy media can be obtained by properly generating inhomogeneous waves. In this work, for the very first time, we demonstrate the physical implementation and the practical relevance of this phenomenon. A thorough numerical investigation of the deep-penetration effects has been performed by designing and comparing three distinct practical radiators, emitting either homogeneous or inhomogeneous waves. As concerns the latter kind, a typical Menzel microstrip antenna is first used to radiate improper leaky waves. Then, a completely new approach based on an optimized 3-D horn TEM antenna applied to a lossy prism is described, which may find applications even at optical frequencies. The effectiveness of the proposed radiators is measured using different algorithms to consider distinct aspects of the propagation in lossy media. We finally demonstrate that the deep penetration is possible, by extending the ideal and theoretical evidence to practical relevance, and discuss both achievements and limits obtained through numerical simulations on the designed antennas.

Effect of Modelling Inhomogeneous Wave Conditions on Structural Responses of a Very Long Floating Bridge

Floating bridges are suitable for connecting land parcels separated by wide and deep waterbodies. However, when the span of the crossing becomes very long, the water environment exhibits inhomogeneities which introduce difficulties to the modelling, analysis and design of the bridge structure. The wave inhomogeneity may be described by means of field measurement and/or numerical simulations. Both approaches face complications when the resolution is much refined. It is thus important to examine the effect of the resolution related to the modelling of inhomogeneous waves on the global structural responses. In this study, a hypothetical crossing at the Sulafjord is chosen, and the wave environment in the year 2015 at 10 positions along the crossing is numerically computed. Next, different inhomogeneous wave conditions are established based on the wave data at 3, 5, and 10 positions, respectively. Time-domain simulations are conducted to examine the effect of different modelling approaches of the inhomogeneous wave condition on the global responses of a long, straight and side-anchored floating bridge.

A Procedure to Calculate First-Order Wave-Structure Interaction Loads in Wave Farms and Other Multi-Body Structures Subjected to Inhomogeneous Waves

A typical assumption when performing analytical, numerical, and experimental studies in wave–structure interaction in multi-body problems such as for wave farms and very large floating structures is the homogeneity of the wave field. Important interactions between the floating elements are dependent on the direction, amplitude, and phase of the waves acting on each. Then, wave homogeneity is probably unrealistic in near-shore areas where these installations are to be deployed. In the present work, an existing interaction method, which allows the use of standard boundary element diffraction codes for solving the first order wave structure linear potential for each unique geometry in the problem, is shown to be able to account for inhomogeneous sea states across the domain of a multi-body problem requiring only minimal modification to its implementation. A procedure to use the method to include arbitrary incoming undisturbed wave conditions at each body is presented. A verification study was done by using an artificial numerical configuration to mimic an inhomogeneous wave field in a standard diffraction code, which was used as a reference. The results obtained using the interaction-method based procedure are shown to be in excellent agreement with the reference ones. Furthermore, an example of frequency inhomogeneity of the wave field in a wave farm is shown and the effects on the motion amplitudes and absorbed power are presented illustrating the applicability of the procedure.

Seismic analysis of a system of dam-massed foundation-reservoir under inclined excitation

One of the acceptable assumptions in engineering practice is vertical propagation of earthquake waves. When the source of earthquake is located very deep in the ground, this assumption is valid, but for sources located in shallow ground, it loses its viability. In this study, linear seismic analysis of a system of concrete dam-massed foundation-reservoir is performed under inclined earthquake excitation. Both P- and SV-type earthquakes are considered for the purpose of the seismic analysis. To consider the effects of inhomogeneous waves for the case of SV wave propagation, post-critical angles are also considered in the analysis. To investigate the effects of earthquake frequency content on the results, three different records with contents of low, intermediate, and high frequencies are selected. Results indicate that considering vertical propagation underestimates the obtained responses. For the case of SV-type earthquakes, post-critical angles must be looked at. Frequency content of the earthquake also has considerable effects on trend and absolute values of responses.

IDENTIFICATION OF NORMAL WAVES FORMING A SOUND FIELD IN A SHALLOW SEA AT THE INFRASONIC FREQUENCY RANGE. Part I

Анализируются результаты экспериментальных исследований звукового поля, зарегистрированного комбинированными приемниками, образующими вертикально ориентированную трехэлементную антенну. Звуковое поле формировалось шумами НИС «Юрий Молоков» в инфразвуковом диапазоне частот. Глубина моря и рабочий диапазон частот исключали возможность возбуждения нормальных волн дискретного спектра в модельном волноводе Пекериса. По результатам спектрального анализа шумового сигнала получена оценка потенциальной помехоустойчивости комбинированного приемника при использовании полного набора информативных параметров, характеризующих энергетическую структуру звукового поля. По результатам анализа вертикальной структуры звукового поля был сделан вывод о том, что звуковое поле сформировано неоднородными нормальными волнами, локализованными на горизонте источника, которые относятся к обобщенным (гибридным) волнам. По результатам анализа вертикального волнового числа, которое принимает чисто мнимые значения в поле неоднородных волн, были получены оценки групповой скорости переноса энергии в рабочем диапазоне частот и выполнена идентификация неоднородных нормальных волн, формирующих суммарное звуковое поле. The results of experimental studies of the sound field recorded by combined receivers forming a vertically oriented three-element antenna are analyzed. The sound field was formed by the noise of the science ship «Yuri Molokov» in the infrasonic frequency range. The depth of the sea and the operating frequency range excluded the possibility of excitation of normal waves of the discrete spectrum in the model Pekeris waveguide. Based on the results of the spectral analysis of the noise signal, an estimate of the potential noise immunity of the combined receiver was obtained using a full set of informative parameters characterizing the energy structure of the sound field. Based on the results of the analysis of the vertical structure of the sound field, it was concluded that the sound field is formed by inhomogeneous normal waves localized at the source horizon, which are referred to as generalized (hybrid) waves. Based on the results of the analysis of the vertical wavenumber, which takes on purely imaginary values in the field of inhomogeneous waves, estimates of the group velocity of energy transfer in the operating frequency range were obtained and identification of inhomogeneous normal waves that form the total sound field was performed.